The ROHC framework, along with a set of compression profiles, was initially defined in RFC To improve and simplify the ROHC specifications, this. Canonical URL: ; File formats: Plain Text PDF Discuss this RFC: Send questions or comments to [email protected] Robust Header Compression (ROHC) is a standardized method to compress the IP, UDP, The ROHC compression scheme differs from other compression schemes, such as IETF RFC and RFC , by the fact that it performs According to RFC , the ROHC scheme has three modes of operation, as follows.
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U, O, or R.
Implementations can use a different structure for and representation of this state. The ROHC algorithm is similar to video compression, in ieft a base frame and then several difference frames are sent to represent an IP packet flow. State transition logic The transition logic for compression states in Bidirectional Optimistic mode has much in common with the logic of the Unidirectional mode. Thus the type needs to be reserved at the framework level.
An IR header contains a profile identifier, which determines how the rest of the header is to be interpreted.
ITU-T work programme
Note that case 3 does not occur in R-mode. Repair of incorrect Rcf updates The CRC can fail to detect residual errors in the compressed header because of its limited length, i.
Padding, segments, and feedback are not allowed in reconstructed packets, so when processing them, steps 14and 5 are modified so that the packet is discarded without further action when their conditions match.
The following algorithm MAY be used: The exact details of how feedback is realized is to be specified in a “ROHC over X” document, for each lower layer X in question.
Note that, as a result of this protocol, there is no way in ROHC to make any use of a segment that has residual bit errors. The CID space is distinct for 395 channel, i.
The transition to R-mode is achieved in the same way. Padding or Add-CID octet Both the compressor and the decompressor start in Irtf. For this, the algorithm of section 5. The most important differences are a more intensive usage of the feedback channel, and a stricter logic at both the compressor and the decompressor that prevents loss of context synchronization between compressor and decompressor, except for very high residual bit error rates.
In order to handle potential decompression errors, the compressor sends periodic refreshes of the stream context to the decompressor. October Learn how and when to remove this template message. The compressor converts the large overhead to only a few bytes, while the decompressor does the opposite.
The procedure for finding the size of the feedback data is as follows: Timeouts, downward ieff When the optimistic approach is taken as described above, there will always be a possibility of failure since the decompressor may not have received sufficient information for correct decompression.
The incorrect decompressed header will then update the context. The packet type is able to carry variable-length feedback information. Actions upon CRC failure This section is written so that it is applicable to all modes. ROHC feedback format Feedback sent on a ROHC channel consists of one or more concatenated feedback elements, where each feedback element has the following format: The compressor is also sending dynamic packet field differences in FO state.
Maximum reconstructed reception unit. However, for ietff other states decompression is not always allowed. Compression logic and packets used U-mode The compressor chooses the smallest possible packet format that can communicate the desired changes, and has the required number of bits for W-LSB encoded values. On the other hand, when the mismatch is caused by a damaged context case 2the decompressor should attempt to repair the context locally. If a feedback channel is available, however, the decompressor MAY send an acknowledgment of successful decompression with the mode parameter set to U send an ACK Istf.
Using this mechanism, the decompressor may be able to repair the context after excessive loss, at the expense of discarding two packets. Optional reference to a channel in the reverse direction. If this cannot be ensured, segmentation should be performed at lower layers.
RFC – RObust Header Compression (ROHC): Corrections and Clarifications to RFC
All RFCs always remain available on-line. These fields are transmitted in a compressed form to save more bits. Alternatives do not place any particular requirements on the ROHC packet type scheme. In general, FO state compresses all idtf fields and most dynamic fields. All segment header packets for one reconstructed unit have to be sent rvc on a channel, i. There are two possible reasons for the CRC failure: This article needs additional citations for verification. If the decompressor receives any of these packets, it will be in sync with the compressor.
It can optionally also communicate the dynamic part of the context, i. Other useful information describing the “Quality” of the document: It is impossible to know for certain which of these is the actual cause.
Robust Header Compression
Other for any supplementary information:. In particular, CIDs for any pairs of forward and reverse channels are not related forward and reverse channels need not even have CID spaces of the same size. The following rules are to be used: If the first bit is 1, the CID uses two octets. Note that the profile parameter determines the syntax and semantics of the packet type identifiers and packet types used in conjunction with a specific context.